Approximately 25,000 intracranial aneurysms rupture each year in North America. The primary purpose of treatment for a ruptured intracranial aneurysm is to prevent rebleeding. There are a variety of ways to treat ruptured and non-ruptured aneurysms.
Possibly the most widely known of these procedures is an extravascular approach using surgery or microsurgery. This treatment is common with intracranial berry aneurysms. The method comprises a step of clipping the neck of the aneurysm, performing a suture ligation of the neck, or wrapping the entire aneurysm. Each of these procedures is formed by intrusive invasion into the body and performed from the outside of the aneurysm or target site. General anesthesia, craniotomy, brain retraction, and placement of a clip around the neck of the aneurysm are typically required in these surgical procedures. The surgical procedure is often delayed while waiting for the patient to stabilize medically. For this reason, many patients die from the underlying disease or defect prior to the initiation of the procedure.
Another procedure--the extra-intravascular approach--involves surgically exposing or stereotactically reaching an aneurysm with a probe. The wall of the aneurysm is then perforated from the outside and various techniques are used to occlude the interior in order to prevent it from rebleeding. The techniques used to occlude the aneurysm include electrothrombosis, adhesive embolization, hog hair embolization, and ferromagnetic thrombosis. These procedures are discussed in U.S. Pat. No. 5,122,136 to Guglielmi et al., the entirety of which is incorporated by reference.
A still further approach is the least invasive and is additionally described in Guglielmi et al. It is the endovascular approach. In this approach, the interior of the aneurysm is entered by use of a catheter such as those shown in U.S. Pat. No. 4,884,575 and U.S. Pat. No. 4,739,768, both to Engelson. These patents describe devices utilizing core wires and catheters, respectively, which allow access to the aneurysm from remote portions of the body. By the use of catheters having very flexible distal regions and core wires which are steerable to the region of the aneurysm, embolic devices which may be delivered through the catheter are an alternative to the extravascular and extra-intravascular approaches.
The endovascular approach typically includes two major steps. The first step involves the introduction of the catheter to the aneurysm site using catheters such as shown in the Engelson patents. The second step often involves filling the aneurysm in some fashion or another. For instance, a balloon may be introduced into the aneurysm from the distal portion of the catheter where it is inflated, detached, and left to occlude the aneurysm. In this way, the parent artery is preserved. Balloons are becoming less favorable because of the difficulty in introducing the balloon into the aneurysm sac, the possibility of an aneurysm rupture due to overinflation of the balloon within the aneurysm, and the risk associated with the traction produced when detaching the balloon.
A highly desirable embolism-forming device which may be introduced into an aneurysm using endovascular placement procedures is found in U.S. Pat. No. 4,994,069, to Ritchart et al. The device, typically a platinum/tungsten alloy coil having a very small diameter, may be introduced into an aneurysm through a catheter such as those described in Engelson above. These coils are often made of wire having a diameter of 2-6 mils. The coil diameter may be 10-30 mils. These soft, flexible coils may be of any length desirable and appropriate for the site to be occluded. For instance, the coils may be used to fill a berry aneurysm. Within a short period of time after the filling of the aneurysm with the embolic device, a thrombus forms in the aneurysm and is shortly thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture. Coils such as seen in Ritchart et al. may be delivered to the vasculature site in a variety of ways including, e.g., mechanically detaching them from the delivery device as is shown in U.S. Pat. No. 5,250,071, to Palermo or by electrolytic detachment as is shown in Guglielmi et al. (U.S. Pat. No. 5,122,136) as discussed above.
Guglielmi et al. teaches an embolism-forming device and procedure for using that device. Specifically, Guglielmi et al. fills a vascular cavity such as an aneurysm with an embolic device such as a platinum coil which has been endovascularly delivered. The coil is then severed from its insertion tool by the application of a small electric current. Desirably, the insertion device involves a core wire which is attached at its distal end to an embolic device by an electrolytic, sacrificial joint. Guglielmi et al. suggests that when the embolic device is a platinum coil, the coil may have a length ranging from 1 cm to 50 cm or longer as is necessary. Proximal of the embolic coil is an insulated core wire or pusher wire, often stainless steel in construction. The core wire is used to push the platinum embolic coil, obviously with great gentleness, into the vascular site to be occluded. The Guglielmi et al. patent shows a variety of ways to link the embolic coil to the core wire. For instance, the core wire is tapered at its distal end and the distal tip of the core wire is welded into the proximal end of the embolic coil. Additionally, a stainless steel coil is wrapped coaxially about the distal tapered portion of the core wire to provide column strength to the core wire. This coaxial stainless steel wire is joined both to the core wire and to the embolic coil. Insulation may be used to cover a portion of the strength-providing stainless steel coil. This arrangement provides for two regions which must be electrolytically severed before the embolic coil is severed from the core wire.
A still further variation found in Guglielmi et al. includes a thin, threadlike extension between the core wire core and the proximal end of the embolic coil. In this way, the core wire does not extend to the embolic coil, but instead relies upon a separately introduced extension.
A continuation-in-part of the Guglielmi et al. patent discussed above, U.S. Pat. No. 5,354,295, describes the use of mechanically detachable embolic devices as well as those which are electrolytically detachable. The embolic devices may be augmented with attached filaments. U.S. Pat. No. 5,540,680, a continuation of U.S. Pat. No. 5,354,295, further describes such mechanically and electrolytically detachable embolic devices. U.S. Pat. No. 5,569,245, a continuation-in-part of the U.S. Pat. No. 5,540,680 patent, adds several new aspects including a new method for electrocoagulation.
A further variation of the Guglielmi et al. device is one in which the distal tip of the stainless steel core wire is crimped onto the proximal end of the embolic device. A simple tapered stainless steel wire extends from the stainless steel pusher wire to the embolic coil.
Taki et al. have devised a variation of the Guglielmi detachable coil using a copper link between the core wire and the coil, described in Treatment of a Spontaneous Carotid Cavernous Fistula Using an Electrodetachable Microcoil, American Journal of Neuroradiology, Vol. 14 (1993).
U.S. Pat. No. 5,423,829 to Pham et al. and U.S. Pat. No. 5,624,449 to Pham et al. describe an electrolytically detachable vaso-occlusive device containing a discrete sacrificial link between the core wire and the vaso-occlusive device to allow clean and quick detachment from the core wire, reducing the possibility of multiple electrolysis sites. The use of extensive electrical insulation about the core wire and sacrificial link as well as the use of scoring on the insulation to focus electrolysis on a targeted, specific site on the link is also taught by Pham et al.
None of the noted procedures using electrolytically detachable embolic devices suggest the structure of the erodable link and related composite core wire described herein.